1. Field of the Invention
The present invention relates to a detection method and detection device and multimedia device, and more particularly, to a detection method and detection device and multimedia device capable of detecting alterations of external devices through a path other than a consumer electronic control (CEC) channel.
2. Description of the Prior Art
High-Definition Multimedia Interface (HDMI) is a full digital transmission interface for images and sounds, and can transmit uncompressed audio and video signals at the same time. HDMI-compatible devices, such as a set-top box, a compact disk (CD) player, a personal computer (PC), a television (TV) game console, a digital stereo, and a TV set, can connect to each other through HDMI-related Transition-Minimized Differential Signaling (TMDS) channels, Display Data Channels and Consumer Electronics Control (CEC) channels. Therefore, HDMI has gradually replaced a conventional analog audio/video transmission interface, such as SCART and RCA terminals.
Please refer FIG. 1, which is a schematic diagram of a conventional HDMI system 10. In the HDMI system 10, HDMI-compatible devices can be categorized into source devices, repeater devices and sink devices according to functionalities. The source devices, such as a CD player, a TV game console, a PC, and a set-top box, are only equipped with HDMI output function, for outputting HDMI signals. The repeater devices, such as a HDMI switch, are equipped with both HDMI reception and output functions, for transferring HDMI signals outputted by the source devices to the sink devices. The repeater devices can transfer signals in single-to-single mode, single-to-multiple mode, multiple-to-single mode, or multiple-to-multiple mode, and may amplify signals at the same time. The sink devices, such as a TV set, a monitor, etc., are only equipped with HDMI reception function, for processing HDMI signals. In addition, if a sink device is equipped with both HDMI reception and transmission functions, a role of the sink device is determined by whether an output of the sink device is connected to an input of another sink device. If another sink device is connected, the sink device performs in the role of a repeater device before the connection is invalid.
In general, an HDMI device is equipped with an independent control interface, such as a remote controller. Under such a condition, if a consumer owns more HDMI multimedia devices, the consumer has to operate more remote controllers, leading to great inconvenience. In this case, a multi-control scheme can be achieved by usage of CEC standard, i.e. using built-in control buttons of another HDMI device in a CEC network to control other HDMI devices on the CEC network at will.
First of all, FIG. 2 is a schematic diagram of a HDMI connector and definitions of pins thereof. As shown in FIG. 2, a pin 13 is used for transmitting a CEC signal. Via the pin 13, a user can control devices supporting HDMI-CEC. For example, the user can utilize a TV set supporting HDMI-CEC to control an external HDMI-CEC DVD player via the pin 13, to perform fast-forward or rewind, or control an HDMI-CEC set-top box to switch channels.
Five categories with twelve devices are defined and each device is assigned with a specific logical address (LA) in CEC standard. As shown in FIG. 3, LA of a TV is “0”, LA of a recording device (such as a DVD recorder) is “1”, “2” or “9”, LA of a tuner is “3”, “6”, “7” or “10”, LA of a playback device (such as a DVD player) is “4”, “8” or “11”, LA or a audio system is “5”. Besides, LA “12” and “13” are reserved for other undefined devices. LA “14” is used for a TV having physical address (PA) not equal to “0000”. LA “15” is unregistered or for broadcasting. The LA is related to a category of an HDMI-CEC device, while the PA is related to topology of HDMI-CEC network, i.e. an address of an HDMI device in HDMI-CEC network. For example, assume that the sink device shown in FIG. 1 is a TV, the LA of the TV is set to “0”, and the PA is set to “0000”.
Furthermore, according to CEC standard, an HDMI-CEC device can send a poll packet to a specific LA, so as to acquire if any device is connected to a CEC network according to whether the LA is occupied. In order to ensure a home multimedia system runs smoothly, even if there is no HDMI device connected to a CEC network, a CEC device (such as a TV set) periodically sends the poll packet as performing synchronization. Under such a condition, a period of sending the poll packets matters to system performance. The period can be either too short such that the system is unnecessarily loaded, or too long such that operating sensitivity of a user interface is affected.
Under such condition, how to enhance detection efficiency of the CEC device without adding system loading becomes an important issue.